Heretofore, in the field of photography or printing by means of a trichromatic separation system using photosensitive color material such as, for example, an RGB analog, RGBTTL, a composite video signal (NTSC) or the like, there is conventionally employed a filter device which inserts filters of the three primary colors, blue, green and red onto the optical axis of a lens group for a predetermined time depending upon the kind or type of original plate or the quality of the photosensitive material, however the filter device of this kind, as shown in FIG. 7, comprises a structure in which a filter 52 is disposed along the optical axis 51 at a position exterior of the lens group 50.
More particularly, a conventional filter 52 was inserted into a diffused light portion along an optical axis 51 so that its aperture .phi..sub.1 is substantially large whereby miniaturization of the associated equipment was difficult to achieve and the response characteristics with respect to the system operation was poor, and also, since it was a separate body from the lens group 50, an exchange of the filter was troublesome which was another disadvantageous problem. Moreover, since the filter 52 was disposed exteriorly of the lens group 50, there were additional problems wherein the filter 52 was directly exposed to the external atmosphere which may contain poisonous gases, fumes or moisture and the like, whereby the filter 52 became deteriorated by means of the foregoing adverse conditions.